It has been known for many years to use bio ethanol refineries to convert biological material into useful chemical products. In a typical bio refinery, a plant material, such as grain containing starch (e.g., wheat or maize), is treated to produce ethanol (so-called “bio ethanol”). The process can be used to produce both potable alcohol and industrial ethanol.
For example, in a conventional bio ethanol plant, wheat is fermented using yeast as the fermentation organism to produce bio ethanol as a main product and by-products, such as animal feed. The ratio of bio ethanol to by-products is approximately 1:1, on a weight basis.
The principle by-product of a bio ethanol plant is called distillers dark grains and solubles (“DDGS”). DDGS is used in the animal feed market, primarily as a feedstock for ruminants. In a conventional process, after the ethanol has been produced by fermentation, it is separated from the fermentation products by distillation.
The residue after distillation of the ethanol (termed whole stillage) is then dried to produce the by-product, DDGS. To aid in drying, the whole stillage is separated into two fractions, a solids fraction and a liquid fraction. This first separation may be carried out in a decanter to produce a solid and a liquid output. The solid output may be pressed into a cake. The liquid output is subjected to evaporation to make a syrup containing, among other things, yeast—this syrup is known as condensed distiller's solubles (CDS). The CDS is then added to the pressed cake and dried to form what is known as the DDGS.
Although the bio ethanol process has been used for many years, very little work has been done on further development of the by-products of the process, and there is very little published information about by-product development.
In a paper by J. Knott and G. Shurson (Effects of feeding diets containing spray dried corn condensed distiller's solubles (CDS) and associated fractions on growth performance of early-weaned pigs), J. Knott, G. Shurson, M. Hathaway, and L. Johnston, J. Anim Sci. Vol 83 (Suppl. 2) p. 71; Ethanol Byproduct may be a diet alternative, National Hog Farmer. Feb. 15, 2005) work was done on the CDS by-product of bio ethanol plants. The authors separated the CDS into two products, yeast cream (YC) and residual solubles (RS). The products were tested for utility as feed additives in animal feed. The purpose of the study was specifically to test whether the by-products of the bio ethanol process had any utility as growth factors.
The Knott/Shurson paper describes subjecting the CDS to a spray drying process to separate the CDS into three fractions, called “sprayed dried distiller's solubles,” “spray dried yeast cream,” and “spray dried residual solubles.” This process would not be suitable for the large scale recovery of yeast, because its cost would be prohibitive. Furthermore, based on the disclosure of the Knott/Shurson paper, there would be no motivation for the skilled person to seek to recover yeast on a large scale, as the paper is concerned with the use of small quantities of yeast as a growth factor present in the mixture, and does not make any reference to the amount of yeast which may be available for recovery from the CDS or the large scale recovery of yeast per se.